Remote control system



June 8, 1943- H. v. ALEXANDERSSON ETAL REMOTE CONTROLSYSTEM Filed April 14, 1941 4 Sheets-Sheet l INVENTOR Cowman? Form? HA/GMS June 8, 1943. H. v. ALEXANDERSSON EI'AL 2,320,995

REMOTE CONTROL SYSTEM Filed April 14, 1941 4 Sheets-Sheet 2 (w/0:11am flora? HA GLE INVENTOR M Z4; 2 I

BY W

n 8, 19 3 H. v. ALEXANDERSSON ETAL 2,320,996-

REMOTE CONTROL SYSTEM Filed April 14, 1941 4 Sheets-Sheet 3 M I Z 5 ATTURNM June 8, 1943. H. v. ALEXANDERSSON ETAL 2,320,996

REMOTE CONTROL SYSTEM Filed April 14, 1941 4 Sheets-Sheet 4 INVENT R' Wwfi' fi Patented June 8, 1943 REMOTE CONTROL SYSTEM Harald Valdemar Alexandersson, Lidingo, and

Carl-Erik Granqvist, Stockholm, Sweden, asslgnors to Aga-Baltie Radio Aktiebolag, Stockholm, Sweden, a corporation of Sweden Application April 14, 1941,.Seria-l No. new In Sweden April 15, 1940 7 Claims.

Our invention relates to remote control apparatus.

In remote control systems it has been proposed to arrange a transmitter in such a way that it transmits a radio-frequency alternating current the frequency of which is determined by the position of the transmitter control, and to arrange a receiver for the transmitted radio-frequency alternating current which is provided with automatic arrangements for tuning to the transmitted frequency, the automatic tuning arrangement being connected to the object to be controlled according to the momentary position of the transmitter control.

In remote control systems of this kind it is suitable to tune the transmitter and the receiver by means of tuning circuits, containing fixed induction coils and variable condensers, the shafts of which are connected to the transmitter control and to the object to be controlled, respectively.

Fig. 1 is schematic diagram of the known arrangement.

Figs. 2 and 3 are diagrams illustrating the operation of the system of Fig. 1;

Fig. 4 is a schematic diagram of a transmitter embodying the present invention;

Fig. 5 is a diagram illustrating the operation of the transmitter of Fig. 4;

Fig. 6 is a schematic diagram of a receiver (or use with the transmitter of Fig. 4;

l"lg.'7 is a diagram illustrating the operation of the receiver of Fig. 6;

Figs. 8 and 9 are diagrams illustrating a novel form of variometer for usein the receiver of Fig. 6; and

Figs. 10 and 11 are schematic diagrams illustrating further embodiments of the invention.

In Fig. 1, 10 is the oscillator valve of the transmitter. valve there is included a coil ii, which is inductively coupled to a coil i2 connected in the grid circuit of the valve Ill, and to a further coil I! connected by a transmission channel II to the receiver. The coil i2 is connected in parallel with a tuning condenser il, mechanically connected to the transmitter control P, shown in the form of a dial. The resonance frequency of the tuned circuit formed by the coil i2 and the condenser M will thus vary with the position of the dial. The circuit l2-H is connected by a grid condenser ii and a grid leak it to the grid circuit of the valve ill to form an oscillating circuit.

The principal parts of the receiver are a modu- In the anode circuit of the oscillatorlator il, a discriminator II, a direct current amplifier 2|, a motor 2i for causing the movement of the secondary parts, to be controlled,

.valve ll contains a cathode 23, an oscillator grid 24, an oscillator anode 25, a, first screen grid 28, a modulator grid 21, a second screen grid 22 and an anode 29.

The oscillator tuning circuit 22, consisting of coil 22 and tuning condenser 33, is connected between the grid 24 and the cathode 23 of the valve it, through a grid condenser 30 and a grid leak II. The oscillator anode 25 is connected to the plus terminal oi the main through a reaction coil 34. By this arrangement oscillations are produced in the internal system of the valve l8, said oscillations being modulated by the oscillations received from the transmitter which are impressed on the control grid 21 of the external system to produce an interference oscillation of beat frequency similar to the operation of superheterodyne radio receivers.

In the anode circuit of the valve ll is included a transformer which is tuned to the beat frequency. This transformer is made as a discriminator, that is, it is sharply tuned to the beat frequency and passes a current the direction and magnitude of which is determined by the variation in signal frequency. One example of such a discriminator is shown in Figure 1. The primary circuit contains the coil 25 shunted by the condenser 20, which can be adjusted to the beat frequency. The secondary circuit contains a corresponding coil 31, shunted by a condenser 30. In addition to the inductive coupling of the two circuits a further coupling is provided by connecting the mid point 0! the coil 31 through a condenser 38 to the high voltage side relative to alternating current, of the coil 25.

The discriminator is completed by two rectiilers l0 and 4|, connected to earth and to the ends of the coil 31 and provided with the shunt resistors 42, 48 and series resistors 44 and 45. For alternating currents the latter resistors are shunted by by-pass condensers l6 and 41. The connection between the resistors 44 and 45 thus is connected to earth while the end terminals of these resistors are connected by conductors l8 and 49 to the grids of direct current amplifying electronic valves 50 and 51, respectively. The anode circuits of the valves 50 and are connected in series with counteracting field windings l2 and 53 of the motor 2| to one terminal of the armature 54 of the motor. the other terminal of which is connected to the plus terminal of the mains. The shaft of the motor is connected to the tuning condenser 33 and also to the object S to be controlled, shown in the form of a dial.

The operation of this system is as follows:

To start with it will be assumed that the trans:

mitter is tuned to a predetermined position on the circuits -36 and 3l-38 are tuned.

In Fig. 2' the voltage vector of the circuit 35-36 is indicated by O-A. The voltage vector of they circuit 31-38 is indicated by B-C. It is well known that at absolute. resonance the voltage vectors of the primary circuit and of the secondary circuit are exactly 90 out of phase relatively to one another. Due to the coupling through the condenser 39 the voltage O-A is added to half the voltage 3-0 in positive direction for application to the rectifier l0, and in negative direction for application to the rectifier ll. The former voltage is thus composed of the vectors O--A and 0-0, while the latter voltage is composed of the vectors O-A and OB. As will be seen from the diagram in Fig. 2 the two resultants O--D and 0-13 in this case are equal. Consequently both rectifiers and ll setup equal but counter-acting voltages over their load resistors, which after amplification in the electronic valves and ii are transmitted to the two windings 52 and 53 of the motor 2 I. The latter is consequently in balance and does not operate.

It will now be assumed that the setting of the transmitter is changed. The condenser I4 is thus shifted and the transmitter frequency is changed either to a higher or to a lower value. The beat frequency will therefor differ from its normal value either in the same direction as the transmitter frequency or in the opposite direction, 0

dependent on whether the frequency of the oscillator'tuning circuit 22 is above or below the transmitter frequency. The direction in which the beat frequency deviates is of no importance as regards the operation, as in every case the direction, is dependent upon the direction of deviation of the transmitter frequency. The beat frequency, however, after the position of the dial P has been changed, is no longer in exact resonance with the circuits 35-36 and 31-33. Hence the two vectors OA and BC will assume a mutual phase position other than perpendicular to one another, and shifted by an angle depending upon whether the frequency displacement has been inductive or capacitive. Withreference to the diagram this may -be most easily explained by assuming that one of the vectors, for example the vector O-A, has turned relative to the other vector 3-0 as indicated by the vector O-A. As will be seen from Figure 2 this causes the resultant OE' of the vector O.A and of the vector 0-0 to become greater than the former resultant O-E of the vectors O--A and OC, whereas on the other hand the resultant 0-D of the vectors O-A' and O-B become less than the resultant 0-D of the vectors O--A and OB. As a result one of the rectifiers 40 or H, for example the rectifier 40, receives a higher voltage and the voltage balance between the load resistors of the rectifiers is destroyed. With a greater voltage drop across the load resistor 44 the grid voltage of the valve 5!) falls and the anode voltage of this valve also fails. Simultaneously the voltage drop across the load resistor 45 decreases so that the grid voltage of the valve 5| rises and the anode current of this valve also rises. Unequal currents flow through the windings 52 and 53 and the motor 54 turns in for example counter-clockwise direction. I

The motor 54 thus changes thesetting of the oscillator condenser 33 and gradually brings this to a value such that the beat frequency is restored to the frequency to which the circuits 35-36 and 3'I38 are tuned.

In these earlier proposed arrangements, however, certain disadvantages are present. For example, the transmitter condenser can only vary from minimum value to maximum value representing for normal condensers a mechanical range of variation of half a revolution. Often. however, this is not sufficient for obtaining the desired range of movement or suflicient precision in the receiver. In such cases it is desirable to make the arrangement capable of operating in such'a way that the control means of the transmitter can be turned more than half a revolution, in many cases even a plurality of revolutions, the controlled means of the receiver thereby turning a corresponding number of revolutions. This is,

however, as explained below, impossible with an arrangement of the kind shown above.

The capacity of a tuning condenser varies during one revolution between a maximum through a minimum and back to the same maximum value. For each revolution of the shaft of the condenser such a cycle of capacity variation is obtained, as shown in Fig. 3 in which the vertical axis represents the capacity and the horizontal axis repre sents the angular setting of the condenser. It may now be assumed that the arrangement is set in a position corresponding to point 55 in Fig. 3 and that a movement is begun from this position in the direction indicated by the arrow 56. The change in transmitted frequency produces a corresponding change in its beat frequency which thus increases or decreases, dependent upon whether the oscillator frequency is above or below the signal frequency. The change in frequency causes an unbalanced voltage to be set up across the two rectiflers, and as a consequence of this voltage the motor is started. The direction of movement of the motor, however, is determined l by relation between the beat frequency and the discriminator frequency. It may now be assumed that the oscillator frequency is higher than the signal frequency. The capacity, rising from the point 55, will then cause a decreasing signal frequency, which will cause an increasing beat frequency and the motor is rotated in a direction to restore the original beat frequency.

After the condenser ll of the transmitter has I minimum point 58. During this period the motor in the receiver will continuously rotate in the opposite direction until it reaches its end position. Hence, if the condenser ll should be turned a plurality of revolutions the receiver would follow the movement of the transmitter during the first half revolution only, rapidly moving back to its initial position during the second half revolution of the transmitter, following the transmitter during its third half revolution, again rapidly returning to the initial position, etc.

The present invention relates to an arrangement by which this disadvantage is obviated. According to the invention the discriminator is arranged in such a way that the control voltage for the remote control motor reverses its direction as the capacity curve of the condenser changes from rising to falling or vice versa. The reversal of the control voltage or current may take place either in the discriminator or in some other place in the control channel. A number of diflerent arrangements of this kind are shown below.

At the moment when the control voltage or current reverses its polarity thisvoltage or current will be zero. Hence, at the point of reversal the system loses its power of following the movement of the transmitter with precision. This disadvantage is obviated according to a further embodiment of the invention by providing two cooperating transmitter units acting upon diii'erent receivers, the discriminators of which are connected to the same remote control motor. The condensers of both of said transmitters, however. are mechanically displaced in relation to each other in such a way that one of the condensers is in a position in which good precision is obtained when the other condenser is in a position of less precision and vice versa.

Fig. 4 shows an arrangement of a transmitter for two frequencies, intended to be connected to a receiver such as that shown in Fig. 6.

The transmitter according to Fig. 4 contains two electronic valves 59 and 60, coupled as oscillators. The oscillation circuits contain one condenser 6l or 62, respectively, and one coil 68 or N, respectively. The cathodes of the electronic valves are connected to taps on the respective coils, whereas the high voltage terminals of the coils are connected to the control grids of the electronic valves over condensers 65 and it, provided with grid leaks "and 88, respectively, in a known manner.

In the anode circuit of each of the valves 59 and 60 is a broadly tuned circuit 89 and 10. respectively, said circuit transferring with substantially the same amplitude all frequencies which may be set up by the oscillator valves. The circuits are coupled to coils H and I2, respectively, which are connected by means of blocking condensers 13, I4 to the transmission mains I! leading to the receiver.

The condensers I and 62 are dimensioned in relation to the coils I and N to tune to a frequency which is not substantially higher than the highest frequency which is to be produced by the oscillator. For obtaining a frequency variation condensers l6 and 11 are connected in parallel to the tuned circuits. These condensers are mechanically connected with each other and with the transmitter control dial 1! as by a common shaft 19. The stators of the two condensers Hi and 11 are displaced in relation to the rotors of the said condensers in such a way that the capacity of one of the condensers is at or near its mean value when the capacity of the other condenser is a minimum or maximum.

The capacity variation oi; the two condensers is shown in Fig. 5, the vertical axis as in Fig. 3 indicating the capacity and the horizontal axis indicating the angular setting of the condenser. The curve ll, drawn in full, shows the variation of the capacity of one of the condensers whereas the dotted curve Ii shows the variation of the capacity in the other condenser.

A receiver for the signal emanating from the transmitter in Fig. 4, is shown in Fig. 6, said receiver being in general substantially the same as the receiver, shown in Fig. l. The transmission mains are indicated at I! as in Fig. 4. Otherwise the same reference numerals have been used as in Fig. 1 except that in the two parts of the receiver of Fig. 6, the hundreds-figures i and 2, respectively, have been added.

The transmission mains I! are connected to both of the receiver units through transformers containing the primary windings I" and 265 and blocking condensers I" and 256. The secondary windings ill and 251 are broadly tuned by the condensers I" and "I to the mean frequency of the received frequency band.

The condenser 33 in Fig. l is replaced in Fig. 6 by two condensers I59 and 25!, and variable condensers I and 2","respectively, coupled in parallel. In the discriminators the inductive coupling is made variable by means of a variometea,

For this purpose the primary and secondary circuits are screened from each other by means of I screens iii and 2H, respectively, and the primary circuits are connected in series with the primary coils I" and 2", respectively, of variometers, the secondary coils of which are formed by the secondary coils I31 and, 23.1, respectively, of the discriminator. Both of the variometers and both of the condensers are connected to a common mechanical control from the motor 54, as indicated by the dotted line II. This mechanical connection is made so that the variometers are at zero coupling when the corresponding condensers pass through their maximum or minimum positions. In Fig. 5 this is indicated by the full line curve ll corresponding to the capacity variation curve of the condenser I60, and by the dotted curve N which corresponds to the capacity variation curve ll of the condenser 280.

By this arrangement an extremely uniform movement of the receiver is obtained. Assuming that the variometers are moving with pure sine variation in coupling, the polar curve for the variation in coupling will be obtained in the form of two circles touching each other. for example the circles I5 and II in Fig. '1 for one of the variometers and, due to the mechanical phase displacement of the circles l1 and 8| for the other variometer. The sum of the coupling voltages through both of the variometers, which also determines the current fed to the field windings 52 and 53 of the motor 54, is then obtained in Fig. 7 in form of the curve which varies only about plus or minus 15% from a true circle as indicated by curve 90.

The operation of the variometers shown in Fig. 6 may cause certain difliculties. as sliding contacts must be avoided due to the small voltages involved, as well as due to the capacity of sliding contacts which may be too high when the higher radio frequencies are used for the control. In

Figs. 8 and 9 an arrangement is shown for obtaining a variometer without using movable contacts. In these figures the coil of the primary circuitin the discriminator is indicated at 9| and the condenser coupled in parallel therewith is in dicated at 92. In series with the coil 9| there is arranged a coil 93. This coil is wound on a cylindrical coil frame in the interior of which is arranged a coaxial cylindrical coil frame carrying a coupling winding 94. This coupling winding is arranged on the same shaft as the primary winding 95 of the variometer, said last named winding being so arranged that upon the rotation of the variometer, a continuous and preferably purely sinusoidal coupling variation to the secondary coil 96is obtained. As a matter of symmetry this last named secondary coil is arranged with a mid point tap and is connected between the two half parts of the secondary winding 91 of the discriminator. The last named winding is finally coupled in parallel with the condenser 98, corresponding to the condensers I38 and 238, respectively. A condenser 99 connects the mid-point on the secondary winding 96 with the primary winding 9|.

In Figs. 10 and 11 two modifications of the arrangement according to Fig. 6 are shown. In the arrangement according to Fig. 6 the two direct current amplifying electronic valves I50 and .I5I and also 250 and 25I, respectively, were so connected to the field windings 52 and 53 of the motor 54, that the sum of the currents flowing through the anode circuits of the electronic valves in question passed through the field windings. At balance'between these currents no movement of the motor was obtained as the two field windings were opposed. The arrangement according to Fig. 10, however, is such that the difference between the voltages created in the two rectifiers is fed-to the field windings. In this case the direct current amplifying electronic valves can be omitted as will be evident from the following.

The coupling from the transmitter to the two modulator valves I and MI is assumed to be made in any manner suitable for the purpose, for example as shown in Fig. 6. The discriminators I02 and I03 are also made in a suitable manner. The discriminator I02 is connected to the two rectifier valves I04 and I05, whereas the discriminator I03 is connected to the two rectifier valves I06 and I01. The direct current voltages from the rectifiers in question across the resistors I00, I09, H0 and III are fed to four resistors H2, H3, H4 and H5, coupled in pairs. The connection point between the resistors H2 and H4 and also between the resistors H3 and H5 are connected to the control grids of amplifier valves H6 and H1, respectively, provided with by-path condensers H9 and I20 and a common cathode bias resistor I2I. The anode circuits are connected in the field windings I48 and I49 of the motor I22. 7

In cases where a high precision is not required this may be substantially simplified. It is primarily possible to make the discriminator itself tunable instead .of using a tunable oscillator circuit to obtain an intermediate frequency adapted to a fixed discriminator. Further only one channel may be used from the transmitter to the receiver instead of two channels and finally it is not necessary to make the reversal of the discriminator voltage continuous, a mechanical switching arrangement being used. An arrangement, simplified in these three respects for receiving a remote control signal is shown in Fig. 11.

The transmission mains I1 from the transmitter, such as the transmitter shown in Fig. 1 are connected to a broadly tuned transformer, the primary winding of which is indicated at I33 and the secondary winding I63 of which is coupled,in parallel with a condenser I64 for tuning approximately to the mean value of the transmitted frequency band. The signal is amplified by means of a standard amplifier valve I65 in the output circuit of which a transformer is connected containing the primary winding I66 and the secondary winding I61. The primary winding is coupled in parallel with a fixed condenser I68 by means of which this circuit is tuned to a frequency within the transmitted frequency range. The secondary winding I61 is coupled in parallel with a condenser I69 by means of which said secondary winding is tunable over the same frequency range as the transmitter. Preferably the condenser I69 is so shaped that the receiver during the automatic tuning always turns through the same angle as the transmitter.

The coils I66 and I61 are connected as described above by means of a condenser I10 for obtaining the discriminator action. The terminals of the coil I 61 are connected to rectifiers I1I and I12 which are connected to load resistors I13 and I14. The connection point between the two load resistors is grounded, whereas the two ungrounded terminals are connected to the control grids of two direct current amplifier valves I15 and I16 by means of two contact arms I11 and I18. The counter contacts forthe contact arms are so arranged that. the contact arms, which are mechanically connected together, when in one position connect the resistor I13 with the amplifier valve I15 and the resistor I14 with the amplifier valve I16 but when in their other position connect the resistor I13 with the amplifier valve I16 and the resistor I14 with the amplifier valve I15. The anode current from the valve n5 flows through the field winding I19 01' the motor I80, whereas the anode current from the valve I16 flows through the field winding I8I.

The shaft I82 of the motor I80 is coupled mechanically to actuate the tuning condenser I69 as well as the switching arms I11I18, so that the arms are switched over from one position to the other each time the condenser I69 passes through maximum or minimum capacity positions. By this arrangement the receiver is prevented from reversing its direction at each half revolution of the transmitter control as in'Fig. 1.

Of course the invention is not limited to the embodiments shown. Various modifications may be made therein as will be apparent to a person skilled in the art.

What is claimed:

7 1. A remote control system responsive to frequency variations of a received signal, comprising a receiver having a circuit responsive to the received signal, arotatable tuning element passnected to cause said motor to continue operation in the same direction in response to continued unidirectional variation in frequency of the received signal as the tuning element passes through its maximum or minimum position.

2. A remote control system responsive to frequency variations of a received signal, comprising a receiver having a circuit responsive to the received signal, a rotatable tuning element passing progressively through maximum and minimum positions during its rotation, said tuning element being connected to control the frequency response characteristics of said receiver, a reversible motor connected to actuated said tuning element, a motor control circuit responsive to the relative frequency characteristics of said receiver and of the received signal and connected and arranged to cause said tuning element to follow variations in signal frequency, and reversing connections connected and arranged to automatically reverse the control of said motor control circuit as the tuning element passes through its maximum or minimum position.

3. A remote control system responsive to frequency variations of a received signal, comprising a receiver having a circuit responsive to the received signal, a rotatable tuning element passing progressively through maximum and minimum positions during its rotation, said tuning element being connected to control the frequency response characteristics of said receiver, a reversible motor connected to actuate said tuning element, a motor control circuit responsive to the relative frequency characteristics of said receiver and of the received signal and connected and arranged to cause said tuning element to follow variations in signal frequency, and reversing connections actuated by said tuning element and constructed and arranged to automatically reverse the control of said motor control circuit as the tuning element passes through its maximum or minimum position.

4. A remote control system responsive to frequency variations of a received signal, comprising a receiver having a circuit responsive to the received signal, a rotatable tuning element passing progressively through maximum and minimum positions during its rotation, said tuning element being connected to control the frequency responsive characteristics of said receiver, a reversible motor connected to actuate said tuning element, a motor control circuit responsive to the relative frequency characteristics of said receiver and of the received signal and connected and arranged to cause said tuning element to follow variations in signal frequency, and reversing connections connected and arranged to reverse the phase of a voltage component of the motor control circuit so as to automatically reverse the control of said motor control circuit as the tuning element passes through its maximum or minimum position.

5. A remote control system responsive to frequency variations of a received signal, comprising a receiver having a circuit responsive to the received signal, a rotatable tuning element passing progressively through maximum and mini- 60 mum positions during its rotation, said tuning element being connected to control the frequency response characteristics of said receiver, a reversible motor connected to actuate said tuning element, a motor control circuit responsive to the relative frequency characteristics of said receiver and of the received signal and connected and arranged to cause said tuning element to follow variations in signal frequency, and reversing connections comprising a variometer connected and arranged to automatically reverse the control of said motor control circuit as the tuning control circuit passes through its maximum or minimum tuning position.

6. A remote control system responsive to frequency variations of a received signal, comprising a receiver having a circuit responsive to the received signal, a rotatable tuning element passing progressively through maximum and minimum positions during its rotation, said tuning element being connected to control the frequency response characteristics of said receiver, a reversible motor connected to actuate said tuning element, a motor control circuit responsive to the relative frequency characteristics of said receiver and of the received signal and connected and arranged to cause said tuning element to follow variations in signal frequency, said motor control circuit comprising a pair of inductive coupling members connected in cascade, one of said members comprising a variometer rotatable with said tuning element, the other of said members comprising coaxial coils the axis of which coincides with the axis of rotation of said variometer.

'7. A remote control system responsive to frequency variations of a pair of received signals which are displaced in frequency and are varied in frequency in the same sense, comprising a receiver having circuits selectively responsive to the two received signals, a pair of rotatable tuning elements passing progressively through maximum and minimum positions, said tuning elements being mechanically connected to rotate in unison and relatively displaced as to their maximum and minimum positions, said tuning elements being respectively connected to control the frequency response characteristics of said receiver circuits, a reversible motor connected to actuate said tuning elements, a motor control circuit responsive to the combined effect of the relative frequency characteristics of said receiver circuits and of the received signals and connected and arranged to cause said tuning elements to followv variations in their respective signal frequencies, said circuits being connected and arranged to cause said motor to continue operation in response to variations in frequency of one of said signals while the tuning element cooperating with the circuit responsive to the other of said signals is passing through its maximum or minimum position.

HARALD VALDEMAR ALEXANDERSSON. CARL-ERIK GRANQVIST. 

